Heretofore, in tire vulcanizing devices, it is conventional to insert an unvulcanized tire into molds, to heat the molds by an outside heat supply arranged outside the molds, and to introduce high temperature steam into the interior of a bladder having been inserted into the tire so that vulcanization is carried out by using the steam as an inside heat supply. In Patent document 1 on a vulcanizing device provided with such an outside heat supply, it is described that passages for flowing a heat medium as an outside heat supply are provided in a mold closing ring member which is arranged around segmented tread molds and segments with the segmented tread molds assembled thereto, to heat the segmented tread molds.